The invention relates to the technical field of textile materials that are thermally insulating and fireproof.
The term xe2x80x9cthermally insulatingxe2x80x9d is used herein to mean textile materials through which heat flux densities are low when the materials are subjected to a temperature gradient.
The term xe2x80x9cfireproofxe2x80x9d is used herein to designate textile materials that are temperature stable, conserving good mechanical properties up to temperatures such as those that result from exposure to 400xc2x0 C.
The invention relates particularly, but not exclusively, to thermally insulating linings for fireproof safety garments.
Numerous vocational activities involve a risk of being burnt directly by a flame, by an electric arc, or by splashes of hot material, or of being burned indirectly by thermal flash.
Amongst such activities, mention should naturally be made not only of firefighters and operators in pyrometallurgy, but also of the activities of the armed forces, police, airplane pilots, racing car drivers, and many others in the fields of chemistry, steel working, glassmaking, the aluminum industry, power generation, or transport, for example.
The garment linings used in these various contexts of activity must not only present good properties in terms of constituting a thermal barrier and withstanding temperature, but they must also present as little an impact as possible on the comfort of the wearer of the garment.
A safety garment that is uncomfortable runs the risk of not always being worn, and a feeling of discomfort can distract attention.
Ideally, the presence of a lining should not give rise to the garment being excessively heavy or bulky.
Also ideally, the presence of the lining should not interfere with the movements of a person nor with the evaporation of sweat.
The problem of disposing of sweat is particularly troublesome given that certain professional activities, such as those of firefighters when fighting a fire, need to be performed in a context of intense physical effort and stress and in geographical areas where the climate is already hot.
This problem is further complicated by the fact that sweating does not occur in a uniform manner over the entire surface of the body.
This problem is particularly serious when accumulated sweat in a garment tends to increase its thermal conductivity, thereby reducing its capacity as an insulating barrier.
The thermal barrier properties of the lining must not simultaneously eliminate all physical sensation of heat, since that sensation is essential.
In particular, the presence of the fireproof insulating lining must guarantee that the length of time between reaching the pain threshold and reaching the threshold of irreversible damage is always greater than the reaction time of a person wearing the fireproof garment.
Conventionally, fireproof thermally insulating linings are made of material that is fibrous and porous.
The use of fibrous and porous materials for making such linings is justified by their heat transfer properties.
This transfer takes place by radiation, by conduction, and by natural convection.
Radiation is the mode of transfer which is usually dominant in fibrous materials, particularly when the temperature gradient to which they are exposed is large.
The conduction flux density depends on the overall porosity of the fiber material, on the area per unit volume of the fibers which is representative of the extent to which the fibers are divided, and on the anisotropy with which the fibers are distributed.
In general, the natural convection flux density is limited in thermally insulating fiber materials.
The insulation obtained by a sheet of fibrous material is generally inversely proportional to the density of the material, to the density of the fibers making it up, and to the thermal conductivity of these components. This insulation is proportional to the thickness of the sheet.
The items described above show that fireproof insulating linings need to satisfy requirements that are varied and sometimes contradictory.
Three examples of such contradictions can be given.
A first example is associated with choosing a value for the porosity of the lining material.
Maximum porosity can be desired for the fibrous and porous material of the lining. The air between the fibers is a medium which is entirely transparent to radiation so only the fibers are involved in diffusing, absorbing, and re-emitting infrared radiation. However maximum porosity can give rise to poor mechanical behavior, in particular during washing and while a garment is being worn, or it can lead to the volume of the lining being excessive, thus impeding the movements of the wearer of the garment.
A second example is associated with selecting a thickness for the lining material.
A thick lining does indeed have a high level of insulating power, particularly with decreasing volume of fiber used per unit volume of the lining. However, a thick lining can impede the movements of the wearer of the garment. In addition, the lining must not be made highly thermally insulating to the detriment of a physical sensation of pain, where the pain threshold varies from one person to another.
A third example is more fundamentally associated with selecting a lining that is highly thermally insulating. Conventionally, putting a thermal barrier into place against temperature gradients going from the outside of the garment towards the inside of the garment automatically leads also to creating a thermal barrier against temperature gradients going from the inside of the garment towards the outside thereof. This can lead to a sensation of discomfort, particularly in hot or desert climates, since removal of sweat and body heat is prevented by the presence of the lining.
The need to remove heat and sweat becomes even more necessary when fireproof safety garments are thick and sometimes heavy.
Conventionally, fireproof safety garments comprise, from their outer face towards their inner face:
an outer cloth, usually based on aramid, usually having a mass per unit area of 200 grams per square meter (g/m3) to 250 g/m3;
a breathing waterproof microporous membrane of the PTFE or phosphorous-containing polyurethane, assembled on a substrate, usually of aramid fibers, or assembled on another layer;
a thermally insulating barrier, usually formed by a non-woven fabric of aramid fibers; and
a cleanliness lining, usually comprising 100% aramid or 50% aramid and 50% fire resistant (FR) viscose, protecting the thermal barrier.
Various embodiments of thermally insulating and fireproof barriers have been proposed in the prior art.
Conventionally, those thermal barriers implement non-woven fabric, woven fabrics, or knits that are thermally stable and non-flammable because of the nature of the fibers used.
The thermal barriers known in the prior art satisfy the needs of their users only partially, in particular concerning their capacity for heat exchange from their inside faces towards their outside faces.
An object of the invention is to propose a fireproof, thermostable, thermally insulating barrier, enabling increased amounts of heat and body sweat to be removed, so as to maintain an impression of a second skin for a person using a garment provided with such a thermal barrier, the barrier nevertheless retaining good properties of protection against fire and against thermal flashes.
To this end, in a first aspect, the invention provides a fireproof and thermostable thermally insulating barrier, in particular for a safety garment, the barrier having a front face for facing an external source of heat or radiation, and a rear face opposite from its front face, said sheet including a plurality of holes each opening out to the front face and to the rear face of said sheet.
The size, the shape, and the density of the holes are such that the natural heat of the human body can be removed more easily, while nevertheless maintaining the thermal barrier effect for sources of heat that are external.
In various embodiments, the sheet is made from a polymer material selected from the group comprising: polyamide imides polyimides (PI) such as P.84, aramids, para-aramids, meta-aramids, polyacrylates, aromatic copolyimides, polyacrylonitriles, polyester-ether-ketone, polybenzimidazoles, polytetrafluorethylenes (PTFE), polysulfones (PSO), polyethersulfones (PES), polyphenylsulfones, and phenylene polysulfides (PPS), mixtures of aramid and polybenzimidazole, thermally stabilized mixtures of polyacrylonitrile and polyamide, polytrifluorochlorethylenes (PTFCE), copolymers of tetrafluoroethene and perfluoroprene (FEP), melamines (e.g. Basofil(copyright)) and phenolic polymers (e.g. Kynol(copyright))
In certain embodiments, the thermal barrier is made from fibers of the above-mentioned polymer materials, or from mixtures of fibers of at least two of said polymer materials.
In particular embodiments, this thermal barrier is made of a composite material provided with a matrix based on a polymer material selected from those mentioned above and reinforcement based on short or long fibers, which can be woven or non-woven.
In various embodiments, these reinforcing fibers are selected from the group comprising metal fibers, glass fibers, xe2x80x9cnon-firexe2x80x9d viscose fibers, carbon fibers, peroxidized carbon fibers, modacrylic fibers.
In a low-cost embodiment, the thermal barrier is made as a composite material reinforced with recycled aramid fibers.
In a second aspect, the invention provides a method of manufacturing a sheet of the kind presented above, the method including a needling step.
In a third aspect, the invention provides a fireproof protective garment, comprising at least one fireproof thermostable thermal barrier as described above.
In certain embodiments, the garment further comprises, going from its outside face towards its inside face: an aramid-based fabric, a breathing waterproof microporous membrane, said fireproof thermostable thermal barrier, and a cleanliness lining.
By way of example, the semipermeable membrane is made from a sheet of phosphorous-containing polyurethane or PTFE, assembled on an aramid fiber substrate.